1. Field of the Invention
The present invention relates to a data communication method for transmitting and receiving data such as characters or images between distant stations, and more particularly, to a data communication method suitable for use as a local area network for transmitting and receiving data in a limited area.
2. Description of the Prior Art
As office automation has been recently progressed, a local area network (LAN) which links various office equipment such as image reading/recording apparatus and word processors through an inexpensive and simple network has been developed. In such an LAN, a number of stations are usually connected to a common communication transmission path, which is shared by the stations communicating with each other. Thus, if communications are initiated concurrently from two or more stations, a so-called "conflict of communication" may occur.
In order to avoid the conflict of communication or to countermeasure a conflict of communication, several network control systems which control the timing of the start of call by the stations in the network have been proposed.
However, none of these systems is a network control system which fully satisfies the utilization requirements of users.
In addition, the proposed network control systems are restricted by a network configuration and have little freedom for expansion of the network or for application to a different network configuration installation.
The local area network is derived from a computer network, but a configuration thereof has been significantly simplified and is different from that of the computer network in order to reduce the cost thereof.
In general, the office equipment connected to the local area network are of a variety of types and have different data output configurations. Accordingly, the waiting time of a station which requests a communication right during communication with another station is indefinite and communication efficiency is low.
When the local area network is expanded or modified, the network control system should be modified. It is very time consuming and ineffective from a cost standpoint to modify individual equipment to be connected to the network.
The communication network may be expanded by linking networks, but it is not advisable from a cost standpoint to introduce a new network control system to link the networks. It is desirable that the stations in the linked network can execute the same configuration of communication as that in the network to which they belong.